Shearing elements have been previously proposed for use in a punch press. For example, U.S. Pat. No. 4,738,173 describes a shearing device for use in a punch press. However, the punch and the die both include two adjacent blades with a specified angle, such as a 90.degree. angle, between them. The punch is square in cross-section with two adjacent edges serving as two cutting blades at right angles to one another. The die has a square opening that receives the square punch head. The square end face of the square punch is inclined at a small angle to provide a high point at the intersection of the two edges. These two edges are used to cut sheet material along two perpendicular lines. A major objective of the present invention is to provide a punch press with a shear assembly for cutting stock along a single line rather than along two lines at right angles to one another.
There are also certain drawbacks in prior equipment. For example, problems can develop if the waste piece is able to bend and remain below the elevation of the lower shear. When this happens, waste material on one side of the cut which is bent down by contact with the shearing blade above it can catch on parts of the press when the sheet is moved for the next cut. This is, of course, unacceptable.
It is the present practice to conduct conventional punching operations on a punch press such as a turret-style press and, after all of the punching operations have been performed, remove the work piece and transfer it manually to a separate machine, namely, a conventional shear for separating pieces from one another. Therefore, it is another object of the invention to provide a shearing tool suited for use in a variety of commercially available punch presses, including turret punch presses, enabling a shearing operation to be conducted on the punch press along with conventional punching operations. In this way, the invention can be used to convert a conventional turret-style punch press station into a shearing station which can be used along with conventional punches present in the press to perform a shearing operation of any length, either before or after a conventional punching operation, and without removing the work piece from the punch press.
It is also an objective of the invention to provide a punch press shearing blade assembly in which two members that reciprocate relative to one another cooperate during use to cut sheet material with a single pair of shearing blades that have only one pair of parallel cooperating shearing edges. It is a further object to provide a reliable provision for seizing and securely holding the sheet material with a forceful grip just prior to and during each successive shearing step. It is another object to find a way of elevating the stock, typically the waste portion of the stock during each return stroke of the shear, so as to guard the shearing edges of both shearing blades and in that way prevent the stock from catching on the shearing blades or other parts. Another object is to provide a pair of spring loaded gripping members on opposite sides of the work piece which grip and securely hold the work piece and at the same time press the work piece toward the exposed face of one of the shearing blades. Another object is to provide a pair of spring loaded, yieldable lower stripper members that are 1) strategically located with respect to the lower shearing blade and 2) are capable of independent movement for dealing separately with the retained or "good" portion of the work piece and the "waste" portion of the work piece on the other side of the cut. A more specific objective is to provide a first pinching or gripping feature for grasping and holding the retained portion of the work piece and a separate, independently operable feature for lifting the other portion, typically the waste portion, of the work piece back to its original undeflected position following each successive shearing step.
A deficiency of prior rectangular punches used for separating parts is the unevenness of the cut produced by removing a series of rectangular waste pieces in rapid succession to produce an elongated cut between two parts. The jagged edge that results requires further processing which is, of course, undesirable. It is and object of the present invention to provide a smooth edge which shows virtually no unevenness and accordingly, requires no further processing to remove discontinuities and produces no waste.
These and other more detailed and specific objects of the present invention will be apparent in view of the following description setting forth by way of example but a few of the various forms of the invention that will be apparent to those skilled in the art once the principles described herein are understood.